Memory element with a magnetically isotropic iron-nickel-copper alloy



Oct. 24, 1967 v J. P. REEKSTIN. JR 3,348,

' MEMORY ELEMENT WITH A MAGNETICALLY ISQTROPIC IRON-NICKEL-COPPER ALLOY7 Filed Dec. 14, 1964 Fe 90] 50 70 60 so 40 50 20 Yo Cu onmr PER CENTmow FIG. 3

ACRYLOID LACQUER 18,000 A 84 Fe-ll cu5N1-7,000A

GOLD 10,000 A lNl/E/VTOP OXYGEN FREE By J. RIREEKST/N, JR.

HIGH CONDUCTIVITY COPPER SUBSTRATE A T TOR/V5 V United States Patent3,348,931 MEMORY ELEMENT WITH A MAGNETICALLY ISOTROPICIRGN-NICKEL-COPPER ALLOY John P. Reekstin, Jr., Madison, N.J., assignorto Bell Telephone Laboratories, Incorporated, New York, N.Y., a

corporation of New York Filed Dec. 14, 1964, Ser. No. 418,094 6 Claims.(Cl. 29183.5)

ABSTRACT OF THE DISCLUSURE The disclosure describes a range of magneticalloy compositions which contain iron, nickel and copper and whichexhibit very low anisotropy. Thisc property makes the alloys especiallyuseful in magnetic memory devices such as the wafile iron memory.Procedures for making these devices are described.

This invention relates to magnetic materials and to devicesincorporating their use.

Magnetic memory devices typically require materials with a largemagnetic anisotropy so that an easy direction exists to provide a simpleand reliable switching pattern. However, an occasional applicationarises in which a reliable square-loop material is desired which isessentially isotropic in magnetic behavior. An exemplary case is foundin the now well-known cubic wafiie-iron memory described and claimed inUnited States Patent 3,274,571, issued Sept. 20, 1966 to A. H. Bobeckand J. L. Smith.

This invention is directed to novel magnetic alloys which provide usefuland favorable magnetic behavior that is essentially equivalent in anycrystal orientation. The invention is defined by a restricted range ofcompositions in the iron-nickel-copper system. The range is defined asfollows:

Wt., percent Fe 8195 Ni 4-6 Cu 1-13 A range of compositions formed toprovide particularly useful properties for the wafile-iron memory deviceis defined as:

Wt., percent Fe 82-88 Ni 4'6 Cu 8-12 A typical magnetic device operatingwith a magnetic film having an alloy composition: 84% iron, nickel, 11%copper revealed the following magnetic characteris- A low anisotropyconstant (less than 1800 ergs/cm. was found to be characteristic of allalloys in the compositional range indicated.

These and other aspects of the invention will become more apparent froman examination of the following detailed description. In the drawing:

FIG. 1 is a ternary phase diagram showing, within the shaded area A, therange of alloy compositions upon which this invention is based;

FIG. 2 is a perspective view partly cut away showing 3,348,931 TatentedGet. 24, 1967 an exemplary device using the magnetic alloy of theinvention; and

FIG. 3 is a schematic representation of a multilayer film useful as theoverlay 14 of FIG. 2.

The alloy compositions falling within the scope of this invention areshown in the shaded region A of FIG. 1. The composition of phases 0c, 7and 7 are described in J. Inst. Metals 67, pp. 189-201.

An exemplary magnetic memory device which advantageously utilizes theisotropic alloys of this invention is shown in FIG. 2. The origin of theterm waflle iron is evident from the configuration of the base plate 10which typically is made from a square-loop ferrite such as Ferroxcube.The word-select winding 11, digit-select winding 12 and sense-winding 13are placed orthogonally in the ferrite slots. The overlay 14, shownpartly cut away, consists of an alloy of this invention. The details ofthe overlay and its fabrication for this particular type of memory unitare described in the following paragraphs. The operation of the deviceand the specific aspects of its over-all construction are detailed inUnited States Patent 3,274,571, issued Sept. 20, 1966 to A. H. Bobeckand J. L. Smith.

A typical wattle-iron baseplate is designed for 64 words with 32 bitsper word or a total capacity of 2048 bits. The overlay has dimensions of1% in. x 2 /2 in. x 0.040 in. and an equivalent storage capacity forabit density of 656 bits/m Each bit occupies an area of 30 mils x 30mils.

The detailed construction of a suitable overlay for the device of FIG. 2is shown in FIG. 3. This is a thin composite film consisting of a 0.04in. copper substrate, a gold film -10,000 A. thick, theiron-nickel-copper alloy -7,000 A. and an insuiating and corrosionprotecting film of Acryloid lacquer -18,000 A.

The gold film and the alloy film are electroplated. The gold film servesto fill surface imperfections and generally a thickness of 8,000 A. to12,000 A. is adequate for this purpose.

The overlay of FIG. 3 was produced in accordance with the followingspecific procedure:

An oxygen-free high conductivity copper substrate is hand-ground with 2/0 and then 4/0 silicon carbide polishing paper until flat, and thenpolished for twenty minutes with an abrasive such as Linde A using ametallographic polishing wheel. This is followed by nondirectionalabrasion of the surafce with 22 micron Carborundum using the wheel. Thelast step serves the following purposes:

(1) The anisotropy constant of the electrodeposited film, althoughsmall, is more accurately reproduced from sample to sample.

(2) The uniformity of the output signals is improved when used as anoverlay in the cubic waflle-iron.

(3) Under nominal operating conditions the ratio of disturbed output toundisturbed output increases. The disturbed output is that which resultsfrom applying a series of opposite polarity bit currents prior toread-out and approximates the minimum output under store conditions.

The substrate is then cleaned with a camel hair brush and an alkalinedetergent to remove the Carborundum particles. The entire operation fromflattening to cleaning normally takes an hour.

Before electroplating, the substrates are etched in a 20% HNO solutionfor fifteen seconds at 25 C. This partially removes the layer ofdisturbed metal on the surface and leads to greater uniformity in thefilm.

The plating line is a four-step process and includes cleaning in alkali,pickling in 20% H 50 gold plating, and finally Fe-Ni-Cu plating. Thealkali serves to remove any dirt or grease that may have gotten on thesubstrate during storage. The pickling removes oxides that formed duringstorage. The gold plating is used to cover many imperfections in thesurface and serves to improve uniformity. The use of gold has alsopermitted salvaging a substrate sincea faulty Fe-Ni-Cu layer can beremoved with dilute HNO without attacking the gold.

The gold plating was accomplished by the following procedure:

Potassium gold cyanide (KAuCN) gms./liter 5.1 Potassium cyanide (KCN)gins/liter" 15.0 Sodium phosphate (NaH PO -H O) gins/liter" 4.0 pH 10.0Temperature C 70 Current density "amps/in?" 0.02 Plating time minutes5.0 Agitation None The Fe-Ni-Cu film isdeposited from an all-chloridebath as follows:

Ferrous chloride (FeCl -4H O) gms./liter 315 The substrates are rinsedthoroughly between steps and are not permitted. to dry. 7

As a final step, the electrodeposited film is coated with.

Acryloid lacquer, chosen because it is easily applied and produces auniform, relatively pin-hole free layer. This layer provides corrosionprotection and electrical insulation of the magnetic film. Anappropriate thickness for this coating is prescribed by the range 13,000A. to 26,000 A. Other. protective coatings found useful are cadmium,zinc, 50-50 nickel-cobalt, chromated zinc, arsenic, trisulfide andsilicon dioxide. However this invention does not,

rely on the specific composition and properties of the film.

These and other aspects of the invention will become apparent to thoseskilled in the art. All such variations and deviations which basicallyrely on the teachings through which this invention has advanced the artare properly considered within the spirit and scope of this invention.

What is claimed is:

1. A magnetic alloy consisting of the composition:

Wt., percent Fe 82 to 88 Ni 4 to 6 Cu 8 to 12 2. A memory elementcomprising a ferrite base plate having raised portions spaced at regularintervals over its surface and defining two orthogonal channels,conductor wires disposed in said channels and an overlay in contact withsaid raised portions and enclosing the conductor wires in the orthogonalchannels, saidoverlay comprising a magnetic alloy havingrthecomposition:

Wt., percent Fe 81 to 95 Ni 4 to 6 Cu 1 to 13 3. The device of claim 2wherein the overlay consists of a copper substrate, a goldfilm overlyingsaid substrate, said magnetic alloy overlying the gold film and aninsulating protective film overlying the magnetic alloy.

4. An isotropic magnetic alloy consisting of the composition:

Percent Fe 84 Ni 5 Cu 11 5. A magnetic overlay for a cubic wafiie-ironmemory element comprising a 40 mil copper substrate, a gold filmapproximately one micron in thickness covering said cop- I persubstrate, and a magnetic film approximately 0.7 micron covering saidgold film, ,Said magnetic film having the approximate composition:

Percent Fe 84 Ni 5 Cu ll 6. The overlay of claim 5 additionallyincluding a protective and insulating film of Acryloid lacquer approxi:mately 2-3 microns in thickness.

References Cited UNITED STATES PATENTS 2,196,824 4/1940 Dahl 75-l25FOREIGN PATENTS 405,643 1/1934 Great Britain.

HYLAND BIZOT, Primary Examiner.

5. A MAGNETIC OVERLAY FOR A CUBIC WAFFLE-IRON MEMORY ELEMENT COMPRISINGA 40 MIL COPPER SUBSTRATE, A GOLD FILM APPROXIMATELY ONE MICRON INTHICKNESS COVERING SAID COPPER SUBSTRATE, AND A MAGNETIC FILMAPPROXIMATELY 0.7 MICRON COVERING SAID GOLD FILM, SAID MAGNETIC FILMHAVING THE APPROXIMATE COMPOSITION: PERCENT FE 5 CU 11